On track-off track tamper



' J. E. ANDERSON ETAL Feb. 10, 1970 ON TRACK-OFF TRACK TAMPER 7 Sheets-Sheet 1 Filed March 18, 1968 S m T N E V .m.

JAMES E. ANDERSON Smou 5.1'Zosasm b 7%11 o% ,WM,MCQMM I Feb. 10, 1970 J. E. ANDERSON ET AL ON TRACK-OFF TRACK TAMPER Filed March 18, 196a 7 Sheets-Sheet 2 &

3| luvsu-roRs JAMES E. Anosasou S 5. I2 oeasm Feb. 10, 1970 ANDERSON ET AL 3,494,300

0N TRACK-OFF TRACK TAMPER Filed March 18, I968 7 Sheets-Sheet 3 INveN'roRS James E. Auosnsou Simon S. Izosasm 0 1970 J. E. ANDERSON ET AL 3,494,300

ON TRACK-OFF TRACK TAMPER Filed March 18, 1968 7 Sheets-Sheet 4 FIG.4 H0

INVENTORS James E. Auosason Swan 5. IZDEBSKI A'r-rvs.

Feb. 10, 1970 J. E. ANDERSON ET AL 3,494,300

0N TRACK-OFF TRACK TAMPER Filed March 18, 1968 7 Sheets-Sheet 5 .42 44, MM, 44am...

Feb. 10, 1970 I J, ANDERSON ET AL 3,49

0N TRACK-OFF TRACK TAMPER Filed March 18, 1968 I 7 Sheets-Sheet 6 Iu-vsu-roas James E. ANDERSON Smart 8. EZDEBSKI 114%., M 4432mm Feb. 10, 1970 J. E. ANDERSON ET AL 3,494,300

ON TRACK-OFF TRACK TAMPER 7 Sheets-Sheet '7 Filed March 18, 1968 nvsu'rons M55 E. Anosnsuu a m. MW m0. om V United States Patent 3,494,300 ON TRACK-OFF TRACK TAMPER James E. Anderson and Simon S. Izdebski, Ludington, Mich., assignors to Jackson Vibrators, Inc., Ludington, Mich., a corporation of Illinois Filed Mar. 18, 1968, Ser. No. 713,961 Int. Cl. E01b 27/00 U.S. Cl. 104-12 20 Claims ABSTRACT OF THE DISCLOSURE An on-track, off-track tamper for railroad track having both rubber-tired wheels, gauged for riding on track rails and suitable for highway travel, and steel flanged track wheels which can be hydraulically lowered to lift a portion of the tamper weight from the tires and hold the tamper firmly on the track. About 20% of the weight of the tamper is floatingly supported on the flanged wheels so that weight transfer remains constant despite relative movement between the wheels and the tamper. The tamper workhead is cantilever suspended to minimize overhanging weight, and is slidably and solidly mounted on a platelike jack beam to be shiftable from rail to rail. The tamper has hydraulic drive and a double pump is valved to pro vide a portion of the available power for start-ups and indexing while full power is delivered at higher speeds for travel.

Description of the invention This invention relates generally to railroad track tamping machines and more particularly concerns a tamper which can be driven on or off railroad track.

Present-day production tampers normally run on the track that is being tamped, both when working and when moving to and from the work location. To clear the track for railroad traflic, special set-off devices or structures are employed to lift the tamper and shift it to one side of the track.

Because it would be obviously desirable to have a tamper capable of running on ordinary roads to the job site, some attention in the past has been given to con structions allowing a tamper to run on either railroad track or paved roads. An example of such a machine as shown in Jackson Patent No. 3,022,744, issued Feb. 27, 1962. The wheel and suspension requirements of relatively high-speed highway travel are, however, quite different from what is needed for an on-track tamper and heretofore machines of this type have enjoyed only limited commercial success.

Accordingly, it is the primary aim of this invention to provide an on-track, off-track tamper having proper suspension and weight distribution for both highway travel and safe, reliable on-track tamping. In more detail, it is an object to provide a tamping workhead that minimizes overhanging weight for highway travel while retaining proper vertical movement of the tamping blades while working. A further detailed object is to utilize rubbertired wheels for both onand off-track drive, but to transfer controlled and uniform portions of the machines weight to flanged wheels for on-track operation so that the machine holds the track properly and provides a solid base for the tamping workhead.

Another object of the invention is to provide a novel hydraulic drive for a tamper of the above kind which efiiciently employs its power for start and stop working movement of the tamper as well as for high-speed travelling movement. A related object is to provide a hydraulic circuit for a tamper of this character which is convenient to control.

It is also an object to provide a tamper having a single rail workhead mounted for quick transfer from rail to 3,494,300 Patented Feb. 10, 1970 ice rail, or to other positions for tamping switches and turnouts, while retaining solid support for the workhead.

Yet another object to to provide a tamper as characterized above which is compact, often using parts for dual purposes, reliable in operation and well suited for economical manufacture.

Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings, in which:

FIGURE 1 is a side elevation of a tamper embodying the invention;

FIG. 2 is a plan view of the tamper shown in FIG. 1;

FIG. 3 is an enlarged fragmentary elevation, partially in section, of a portion of the tamper shown in FIG. 1;

FIG. 4 is an enlarged fragmentary elevation of another portion of the tamper shown in FIG. 1;

FIG. 5 is an elevation taken approximately along the line 55 in FIG. 4;

FIG. 6 is a fragmentary elevation taken approximately along the line 66 of FIG. 1;

FIG. 7 is a fragmentary view taken approximately along the line 77 in FIG. 6;

FIG. 8 is an enlarged fragmentary view taken approximately along the line 8-8 in FIG. 1;

FIG. 9 is an enlarged fragmentary view taken approximately along the line 99 in FIG. 1; and

FIG. 10 is a schematic hydraulic diagram of the circuit utilized in the tamper of FIG. 1.

While the invention will be described in connection with a preferred embodiment, it will be understood that we do not intend to limit the invention to that embodiment. On the contrary, we intend to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

Turning now to FIGS. 1 and 2, there is shown a tamper 10 embodying the invention and running on railroad track rails 11. The tamper 10 includes a frame 12 supported on the rails 11 by both rubber-tired wheels 13 and 14 and flanged steel Wheels 15 and 16. A tamping workhead 17 is positioned at one end of the frame 12 and a housing 18 enclosing a power plant, electrical generator and hydraulic circuit components is located at the other end of the frame. An operators platform 19 is positioned on the frame 12 between the workhead 17 and the housing 18.

The tamper 10 illustrated is a jack tamper with a pair of rail clamps 21 (see FIGS. 3 and 10), a pair of hydraulic jacks 22, and a workhead subframe 23 suspending a plurality of vibratory motors 24 with depending tamping blades 25. In tamping operation, the rail clamps 21 grip the rails 11, the jacks 22 engage the road bed outside of the rails and lift the track, and the tamping blades 25 are then driven into the ballast about either rail, the workhead 17 being shiftable from side to side so as to work alternately about one rail or the other.

In carrying out the invention, both the flanged Wheels 15, 16 and the rubber-tired wheels 13, 14 are gauged to ride on the rails 11 of the railroad track and. when riding on the track and tamping, the flanged wheels 15, 16 are hydraulically forced against the track so that a predetermined portion of the total tamper weight is trans ferred from the rubber-tired wheels to the steel flanged wheels. For off-track, highway travel, the flanged wheels 15, 16 are hydraulically raised and the tamper 10 runs on the rubber-tired wheels 13, 14 as a conventional vehicle. The wheels 13 are driving wheels for both on-track and otf-track movement of the tamper. Off-track, the rubber-tired wheels 14 are steering wheels. On-track, the flanged wheels 15, 16 hold the tamper solidly on the track.

As a feature of the invention, a reversible seat 31 is mounted centrally on the operators platform 19, being pivoted in an upstanding post 32, and a set of drive and workhead controls 33 are positioned between the seat 31 and the workhead 17, and a set of drive and steering controls 34 are positioned between the seat 31 and the housing 18. As seen in FIGS. 1 and 2, the tamper appears riding on track with the seat 31 facing the workhead. In this case, the operator utilizes the control set 33 to drive the tamper to the left and manipulate the tamper blades 25. When going off the track, the workhead 17 is raised to a travel position, the flanged wheels 15, 16 are lifted, the seat 31 is reversed, and the operator utilizes the control set 34 to drive the tamper 10 much as any conventional vehicle.

The rubber-tired drive wheels 13 are mounted on a fixed driven axle 36 but, to give some off-track riding smoothness, the rubber-tired steering wheels 14 are journalled at opposite ends of an axle 37 which is pivoted at 38 (see FIG. 8) on the tamper frame 12 for tilting movement about a fore-and-aft axis along the approximate center line of the frame. The wheels 14 are pivoted for steering on king-pin assemblies 39 which are interconnected by a tie rod 41. A two-way linear hydraulic actuator 42 anchored to the axle 37 steers the wheels 14. The pivot 38 provides some float in the off-track vehicle suspension that reduces the harshness of the otherwise springless support. Of course, the rubber tires on the wheels 13, 14 also soften off-track travel.

In accordance with the invention, the flanged wheels 15, 16 have individual actuators 41 and 32, respectively, with a common hydraulic circuit for driving the flanged wheels against the rails, and pressure is maintained in the common circuit so that a predetermined weight transfer is floated onto the flanged wheels and maintained despite relative vertical movement between the frame 12 and the steel wheels 15, 16. As shown more particularly in FIG. 10, a source of fluid under pressure including a pump 43 driven by an engine 44, constituting the power plant for the tamper 10, circulates fluid from a sump tank 45 through a pair of three-position valves 46 and 47 back to a sump return manifold 48. The valve 46 is detented and stays in the position to which it is manually shifted. Shifting the valve to the right in FIG. 10 pressurizes a circuit 49 that retracts the actuators 41, 42 and raises the flanged steel wheels. With the circuit 49 pressurized, a pilot line 51 opens a check valve 52 to permit fluid to be returned to the sump tank 45 from the tops of the actuators 41, 42 through a return line 53. A pressure limiting valve 54 relieves the circuit 49 when the wheels 15, 16 are fully raised.

When the valve 46 is shifted to the left as seen in FIG. 10, a second circuit 55 is pressurized and fluid, through the check valve 52, extends the actuators 41, 42 to drive the flanged wheels 15, 16 against the rails 11. An accumulator 56 and a settable unloading valve 57 act to maintain a constant pressure in the circuit 55 behind the check valve 52. A pair of shutoff valves 58 and 59 are normally open so that the weight borne by the flanged wheels 15, 16 is floated on the fluid in the circuit 55. The tamper 10 can rock relative to the flanged steel wheels, and the wheels can conform to minor variations in track rail height, without changing the amount of weight transfer.

It has been found desirable to set the valve 57 so that approximately 20% of the total tamper weight is transferred to the flanged steel wheels 15, 16, leaving about 80% of the total weight supported by the rubber-tired wheels 13, 14. The 20% weight transfer causes the tamper 10 to firmly hold the track, while the 80% load gives adequate traction to the drive wheels 13 for moving the tamper 10 along the track.

As another feature, the actuators 41 are of larger diameter than the actuators 42 so as to approximately equalize the loading on the rubber-tired wheels 13, 14 despite the overhanging weight of the workhead 17. The larger diameter actuators 41 cause the flanged wheels 15 at the workhead end of the frame 12 to carry a greater load than the other pair of flanged wheels 16 at the uniform pressure maintained in the circuit 55. As a result, the rubbertired wheels 13, 14 aer approximately equally loaded and the tamper 10 is more stable on the track and provides a more solid base for the workhead.

A further feature of the arrangement of the valves 46, 47 lies in the use of the valve 47 for controlling the tamper steering actuator 42. With the valve 46 centered, manually shifting the valve 47 to the left or right as seen in FIG. 10 swings the steering wheels 14 to one side or the other. However, if the valve 46 is not in centered position, fluid under pressure cannot reach the valve 47 and hence the wheels 14 cannot be inadvertently turned. This avoids having the wheels 14 turned while the flanged wheels 15, 16 are being held down under pressure and the tamper is riding on the track rails 11. Therefore, after driving the tamper 10 from a road onto the track and straightening the steering wheels 14, a shutoff valve 61 can be closed to lock the steering wheels in position but, in any event, fluid will not be available to turn the wheels 14 when the valve 46 is manipulated to control the flanged wheels 15, 16.

With the circuit to the flanged wheel actuators 41, 42 being common, it is desirable to make some provision for preventing the two actuators at either side of the tamper 10 from accepting all of the fluid when the circuit 55 is pressurized and thus tipping the tamper to one side or the other. In carrying out this aspect of the invention, the wheels 16 are journalled on a rigid beam 62 (see FIG. 9), to the ends of which the actuators 42 for these wheels are pivoted. A second beam 63 is disposed parallel to the beam 62 and is mounted for vertical movement on the frame by means of posts 64, fixed at each end of the beam 63, which are slidably received in sleeves 65 anchored on the frame 12. The beam 62 is pivoted at 66 on the beam 63 for tilting movement about a fore-and-aft axis midway between the flanged wheels 16. Thus, while the tamper 10 and the beam 63 can rock about the pivot 66 relative to the flanged wheels 16 and the axle beam 62, the fact that the beam 63 will not rock relative to the tamper frame 12 prevents the wheels 16 from being driven down against the rails 11 unless pressure is developed in both of the actuators 42. This avoids tilting the tamper 10 sidewards when fluid is directed to the common circuit 55 and assures that all of the actuators 41, 42 are uniformly pressurized.

Pursuant to one aspect of the invention, the workhead 17 is mounted solidly, but slidably, on a strongback 70 formed as a thick, generally rectangular, plate-like body disposed transversely at the workhead end of the tamper frame 12. The workhead 17 includes a carrier 71 (see FIGS. 3 and 5) having an upper portion embracing the top edges of the strongback 70 and a lower portion embracing a rail 72 fixed by brackets 73 to the lower portion of the strongback. One set of bearing members 74 is mounted on the carrier 71 to slidably engage the top, front and back of the strongback 70, and another set of bearing members 75 is mounted on the carrier to slidably engage the front and back of the rail 72. Preferably, the bearing members 74, 75 are formed of a resinous composition with a low coeflicient of friction, such as nylon, and are impregnated with a lubricant such as molybdenum.

To prevent upward movement of the workhead 17 relative to the strongback 70, as when the tamping blades are being driven down into the ballast, the rail 72 is T-shaped and the bearing members 75 engage the underside of the horizontal portions of the rail. It can thus be seen that the carrier 71 is slidably but solidly carried on the strongback 70 with the bearing members 74, 75 restricting movement in all directions but transversely along the strongback.

In order to position the workhead 17 transversely relative to the rails 11, a small reversible hydraulic motor 76 is mounted on the carrier 71 and connected, by a chain 77, to a sprocket cluster 78 journalled in the carrier 71. A second chain 79 extends the length of the strongback 70 and has its ends secured to brackets 81 (see FIG. 2). Between its ends, the chain 79 is trained about three sprockets 82, 83 and 84 journalled on the carrier 71 (see FIG. and the sprocket 83 is part of the cluster 78. Thus, operating the motor 76 causes the carrier 71 to pull itself along the chain 79, the carrier sliding freely on the strongback 70 and its rail 72. The bearing members 74, 75 insure that wherever positioned, the workhead 71 is firmly supported on the strongback.

When tamping, the strongback 70 rides directly on the rails 11 and for this purpose is provided with rollers 87 journalled in brackets 88 on the outer face of the strongback 70 (see FIGS. 2 and 3). The strongback 70 serves as a track jack beam and supports both the rail clamps 21 and the hydraulic jacks 22. For travelling, the strongback 70 is raised to a travel position and, tomount the strongback for vertical movement on the tamper frame 12, the strongback has double arms 91 which embrace frame members 92 fixed on the end of the frame 12. The members 92 have upper and lower vertical slots 93 and the arms 91 carry rollers 94 which ride in the slots, thus guiding the strongback 70 for up and down movement and also providing a connection permitting the tamper to push the strongback 70, when in lowered tamping position, along the track rails 11.

Another feature of the invention lies in using the flanged wheel actuators 41 for shifting the strongback 70 between working and travel positions. For this purpose, each of the wheels is mounted on a short axle 96 (see FIGS. 3 and 6) secured in a bracket 97 that is pivoted at 98 on flanges 99 extending downwardly from the frame 12. The actuators 41 interconnect the frame 12 and the brackets 97 so that the wheels 15 are moved vertically by swinging the brackets 97 about their pivots 98. The strongback 70 carries a pair of supports 101 having lower bifurcated portions adapted to ride on the axles 96 so that raising and lowering the flanged wheels 15 with the actuators 41 shifts the strongback 70 and the workhead 17 between working and travel positions. By slipping pins in holes 102 at the top of the double arms 91 when the strongback is in raised travel position, the pins can abut the tops of the frame members 92 and releasably lock the strongback and the workhead 17 in travel position. The wheels 15 are then lowered with the axles 96 moving freely from the supports 101 so that a portion of the tamper weight is again borne by the wheels 15 for on-track travel of the tamper 10.

Thus, looking at the FIG. 10 circuit, when it is desired to lift the workhead 17 and travel along the track, the shutoff valve 59 is closed and the valve 46 shifted to the right as seen in that figure. The closed valve 59 holds the flanged wheels 16 on the track, but the actuators 41 lift the wheels 15 and the strongback 70 to its travel position. The strongback is locked up by placing pins in the holes 102, and the valve 46 is then shifted back to the left so as to lower the wheels 15 and re-establish the desired weight transfer. The shutoff valve 59 is then opened and the tamper is ready for on-track travel.

Pursuant to the invention, the effect of the overhanging workhead weight is minimized by supporting the tamping motors 24 cantilever fashion while providing for proper up and down movement of the tamping blades 25. In the illustrated construction, the workhead carrier 71 includes a substantially vertical column 104, and a post 105 is secured to the subframe 23 in substantially parallel relation to the column 104. A bell crank 106 is pivoted at 107 on the column 104, and one arm of the bell crank 106 extends away from the frame to support the post 105 at a pivot 108. An actuator 109 is anchored on the carrier 71 and is pivotally connected at 110 to the other end of the bell crank 106. A link 111 is pivoted at 112 and 113 on the column 104 and the post 105, respectively, so as to create, with the post, column and bell crank 106, a parallelogram linkage that keeps the tamping blades 25 properly oriented during up and down tamping movement of the subframe under power of the actuator 109. With this construction of the workhead, a minimum amount of weight is suspended out from the tamper frame and this enhances the off-track riding qualities of the tamper.

Tampers are often operated under automatic, or semiautomatic, control of the kind shown in US. Patent No. 3,270,690 issued Sept. 6, 1966, in which a rail height indicating device, such as a light mask 115 with a central slot 116 (see FIGS. 1 and 6) rides the rails 11 to indicate the effect of the jacks 22 on the elevation of the track. As another feature of the tamper 10, the mask 115 utilizes the flanged wheels 15 as rail followers. For this purpose, the mask 115 is secured to an inverted U-shaped frame 117 which floats freely up and down in sleeves 118 secured at each side of the tamper frame 12 closely adjacent the strongback 70. Each lower end of the frame 117 carries a bifurcated shoe 119 adapted to ride on the axles 96 of the flanged wheels 15. Thus, when it is desired to use the rail height indicating mask 115, the frame 117 is simply lowered onto the axles 96 and the flanged wheels 15 serve as rail followers shifting the mask 115 with up and down movement of the rails 11.

The tamper 10 is driven both on-track and off-track by a reversible hydraulic motor (see FIG. 10) coupled to the drive wheels 13 and which is powered by fluid from a circuit 126. Preferably, the circuit 126 delivers fluid to a pair of parallel forward and reverse valves 127 and 128, each associated with a safety release valve 129, with the valve 127 being in the control et 33 and the valve 128 being in the control set 34. The valves 127, 128 are identical except that the valve 127 is spring centered to normally dump fluid from the circuit 126 through a line 131 to the sump tank 45, while the valve 128 is detent held in any one of its three positions. Thus, when the operator is tamping and using the control set 33, the valve 127 must be manually held to drive the tamper. But, for off-track travel, the operator uses the valve 128 in the control set 34 so that the circuit 126 remains open to the motor 125 in either forward or reverse direction without continuous manual pressure and the operator can concentrate on steering or otherwise controlling the tamper.

Both valves deliver fluid to the motor 125 through a brake valve assembly 133. The brake valve assembly 123 insures that the drive motor 125 stops when fluid flow stops, whether in forward or reverse direction, and without the motor becoming a pump driven by movement of the tamper. Thus, the assembly 133 includes valves 134 which by-pass check valves 135 to exhaust fluid from the motor 125 only if pilot lines 136 are pressurized on the opposite side of the motor. If fluid under pressure is not being delivered to the motor 125, the valves 134 close, blocking the fluid flow from the pump and thus braking the tamper.

More conventional, hydraulically actuated brakes (not shown) are operatively associated with the drive axle 36 for use during off-track, highway travel, and these brakes are also useful in assisting the hydrostatic brake described above, particularly in holding the tamper 10 on a track grade.

As another aspect of the invention, a double pump 141 and 142 giving two independent outputs is arranged With one output going directly to the tamper drive motor circuit 126 and the other output going to the circuit 126 under the control of an unloading valve 143. The pump 141, 142 is driven by the tamper engine 44 and draws fluid from the sump tamp 45. The pump 141 delivers fluid t a circuit 144 including a pair of three-way valves 145 and 146 which, when centered, allow fluid to go directly to the circuit 126. The pump 142 delivers fluid to a circuit 147 including a pair of three-way valves 148 and 149 which, when centered, allow fluid to reach the unlOading valve 143. Both circuit 144, 147 include system pressure limiting valves 149.

The unloading valve 143 is controlled by a pilot line 151 which is open to pressure in the circuit 144. When the tamper is stopped and one of the valves 127, 128 is moved to start the motor 125, there is relatively high pressure in the circuits 144, 126 until the inertia of the tamper 10 is overcome and the machine begins moving. This high pressure, conveyed by the pilot line 151, keep-s the unloading valve 143 open and dumping fluid from the circuit 147 to the sump manifold 48. Once the tamper is underway and pressure in the circuits 144, 126 drops, then the valve 143 is closed and the output of the circuit 147 is added to the circuit 126 so that the total volume of both pumps 141, 142 is available to drive the tamper. This gives a sort of two-speed transmission effect, preventing full power from being initially applied to the drive wheels, which would cause drive wheel slippage at start-up, and also avoiding the build-up in the system of excessive power, and heat, accompanied by undue laboring of the tamper engine 44.

As another feature of the hydraulic circuit, the workhead traversing motor 76 is controlled by the valve 148 in the circuit 147, while the alternate circuit 144 is used to start the tamper drive motor 125. Movement of the valve 148 up or down as seen in FIG. 10 causes rotation in the motor 76 in one direction or the other so as to drive the workhead 17 to one side or the other of the strongback 70. Since independent circuits traverse the workhead and drive the tamper in start-up operation, the tamper operator can index the tamper forward to the next tie to be tamped while simultaneously traversing the workhead to the opposite rail.

The workhead raising and lowering actuator 168 is controlled by the valve 146 and movement of this valve either up or down as seen in FIG. 10 causes the actuator 109 to be extended or retracted and thus raise or lower the tamping blade 25. The actuator 109 is protected by a relief valve 152. The valves 145, 149 are three-way valves which control the jacks 22 and the rail clamps 21 through sequence valves 153. The sequence valves 153 insure that the clamps 21 tightly grip the rails 11 before pressure in pilot lines 154 opens the valves 153 and drives the jacks 22 downward. Because of the series arrangement of the valves 145, 146 and 148, 149, simultaneous manipulation of the workhead and the track jacks is not possible. Also, operation of the tamper motor 125 is dependent upon the valves 145, 146 being centered.

In the preferred embodiment, an emergency pump 156 driven by an electric motor 157, which can be powered by the starting battery for the tamper engine 44, is arranged to draw fluid from the sump tank 45 and deliver the fluid, through control valves in an assembly 158, to supplement or replace the outputs of the pump 43 and the sections 141, 142 of the double pump.

We claim as our invention:

1. A tamper comprising, in combination, a frame having rubber-tired wheels gauged to ride the rails of railroad track, means on said frame for driving and steering said rubber-tired wheels, a tamping workhead at one end of said frame and adapted to tamp the track on which the tamper rides, a first pair of flanged wheels gauged to ride the track mounted on said frame at the workhead end, a second pair of flanged wheels mounted on said frame gauged to ride the track at the non-workhead end of the machine, a hydraulic actuator for each of said flanged wheels mounted on aid frame and adapted to lift the flanged wheels from the track and force the wheels against the track so as to shift tamper weight from said rubber-tired wheels to said flanged wheels, a common hydraulic circuit for said actuators, and means for pp y g hy raulic fluid to said circuit at a fixed pressure so that a predetermined fraction of the total tamper weight is floated onto said flanged Wheels and maintained despite relative movement between said frame and said flanged wheels.

2. The combination of claim 1 in which said workhead makes the workhead end of said frame heavier than the non-workhead end, and said actuators for said first pair of flanged wheels are larger than the actuators for said second pair of flanged wheels so that with said fixed pressure said first pair of wheels carries a greater load than the second pair and said rubber-tired wheels are approximately equally loaded.

3. The combination of claim 1 including a first beam mounted for vertical movement on said frame, a second beam disposed parallel to said first beam, said second pair of flanged wheels being joumalled at the ends of said second beam and said actuators for said second pair of flanged wheels being connected near the ends of said second beam, and said second beam being pivoted on said first beam for tilting movement about a fore-and-aft axis midway between the second pair of flanged wheels.

4. The combination of claim 1 in which said workhead includes a subframe suspending a plurality of tamping blades, a substantially vertical post secured to and extending upwardly of said subframe, a column mounted on said frame in substantially parallel relation to said post, a bell crank pivoted on said column and having one arm extending away from said frame to pivotally support said post, an actuator on said frame connected to the second arm of said bell crank so that said actuator can pivot the bell crank and thus raise and lower said sub frame, and a link extending between pivots on said post and said column to create, with the post, column and bell crank, a parallelogram linkage keeping said tamping blades properly oriented during up and down movement of said subframe.

5. The combination of claim 1 in which said rubbertired wheels include a pair of steering wheels journalled on opposite ends of an axle, said axle being pivoted on said frame for tilting movement about a fore-and-aft axis along the approximate center line of the frame.

6. The combination of claim 1 including an operators platform on said frame, a reversible seat mounted centrally on said platform, a set of drive and workhead controls positioned on said frame between said seat and said workhead, and a set of drive and steering controls positioned on said frame between said seat and said non-workhead end of the frame.

7. The combination of claim 1 including track jacks mounted on said frame adjacent said workhead, a device for indicating the height of the track rails in an automatic control system, said device being mounted for up and down floating movement on said frame, and said device having bifurcated shoes adapted to ride on the axles of said first pair of flanged wheels so that these flanged wheels also serve as rail followers for said device.

8. The combination of claim 1 in which said workhead includes a strongback extending transversely of said frame, said strongback being mounted on the workhead end of said frame for vertical movement between a lowered working position and a raised travel position, one of said first pair of flanged wheels having an axle movably mounted on said frame, a support on said strongback having a lower portion adapted to ride on said axle so that raising or lowering said one flanged wheel shifts the strongback between said working and travel positions, means for releasably locking said strongback in travel position so that said first pair of flanged wheels can be lowered into track engaging, load bearing position with the strongback remaining in travel position.

9. The combination of claim 8 including jacks mounted at each end of said strongback so that the strongback serves as a track jack beam when lowered into working position.

10. In a tamper, the combination comprising, a frame mounted for movement along railroad track, a strongback mounted on one end of said frame transversely of the track, said strongback being formed as a thick generally rectangular body, a workhead carrier mounted on said strongback for movement along said strongback transversely of the track, said carrier having a portion embracing the top edges of the strongback, bearing members mounted on said portion in sliding engagement with the top, front and back of said strongback, a rail fixed to the lower portion of said strongback, said carrier having a lower portion embracing said rail, bearing members mounted on said lower portion in sliding engagement with the front and back of said rail, and means for positioning said carrier along said strongback.

11. The combination of claim in which said bearing members are formed of a resinous composition with a low coefiicient of friction and impregnated with lubricant.

12. The combination of claim 10 in which said rail is T-shaped and said bearing members on said lower portion also engage the horizontal portions of said rail to prevent upward movement of said carrier on said strongback.

13. The combination of claim 10 including a subframe suspending a plurality of tamping blades, a substantially vertical post secured to and extending upwardly of said subframe, said carrier including a column disposed in substantially parallel relation to said post, a bell crank pivoted on said column and having one arm extending away from said frame to pivotally support said post, an actuator on said carrier connected to the second arm of said bell crank so that said actuator can pivot the bell crank and thus raise and lower said subframe, and a link extending between pivots on said post and said column to create, with the post, column and bell crank, a parallelogram linkage keeping said tamping blades properly oriented during up and down movement of said su bframe.

14. In a tamper having sets of both rubber-tired wheels and vertically movable flanged Wheels riding on the track, the combination comprising, a two-way hydraulic actuator for each of said flanged wheels, a source of fluid under pressure, a first circuit for directing fluid from said source to the side of said actuators causing the flanged wheels to be raised, a second circuit for directing fluid from said source to the side of said actuators causing the flanged wheels to be driven against the rails, said second circuit being a common circuit so that the pressure remains the same in each actuator despite relative movement between the tamper and the flanged wheels, means for maintaining a predetermined pressure in said second circuit, and a valve for shutting off or directing a flow of fluid between said source and either said first or second circuits.

15. The combination of claim 14 in which said rubbertired wheels include tamper driving wheels and said predetermined pressure is sufiicient to cause the flanged wheels to bear approximately 20% of the tamper weight while the rubber-tired wheels bear the remaining approximately 80%.

16. The combination of claim 14 including a hydraulic actuator and control for steering said rubber-tired wheels, said valve being effective to direct fluid from said source to said actuator and control only when the valve is shutting ofl fluid flow to both said first and second circuits.

17. In a tamper having a first hydraulic motor for driving the tamper along the track and a single workhead movable transversely of the track under the power of a second hydraulic motor, the combination comprising, a source of hydraulic fluid under pressure including a double pump giving two independent outputs, a first circuit including a control valve connecting one of said outputs to said first motor, and a second circuit including a control valve connecting the other of said outputs to said second motor so that the tamper can be driven forward while the workhead is simultaneously moved transversely.

18. The combination of claim 17 in which said second circuit is connected to said first circuit through an unloading valve that dumps said other output to pump when said second motor is not being driven, said unloading valve being responsive to a drop in pressure in said first circuit so that both outputs are directed to said first motor at lower running pressures but only said first circuit drives said first motor at higher start-up pressures.

19. In a tamper having a hydraulic motor for driving the tamper, the combination comprising, a source of hydraulic fluid under pressure including a double pump giving two independent outputs, a first circuit connecting one of said outputs to said motor, and a second circuit including an unloading valve connecting said other output to said first circuit, said unloading valve being normally effective to discharge said second output to pump but responsive to a drop in pressure in said first circuit so that both outputs are directed to said motor at lower running pressures while only said one output drives the motor at higher start-up pressures.

20. The combination of claim 19 in which a pair of forward and reverse valves are interposed in said first circuit for controlling fluid flow to said motor, said valves being connected so that operation of either valve controls the motor independently of the other valve, one of said valves being spring biased to a neutral, motor-off position so that continuous manual pressure is required to operate the motor, and other of said valves being releasably held when manually shifted to an operating position so that continuous manual pressure is not required to operate the motor.

References Cited UNITED STATES PATENTS 1,861,655 6/1932 Brosig 104-12 2,655,873 10/1953 McDonald.

2,789,516 4/1957 Hursh et al. 104-l2 2,976,815 3/1961 Bean l0412 3,022,744 2/1962 Jackson l0412 ARTHUR L. LA POINT, Primary Examiner R. A. BERTSCH, Assistant Examiner 

